Other guidance systems -- both on the ground and aboard the
rocket -- worked well, said a senior military official.

The official compared the test to finding a house. "You
start off with the satellite sensors telling you the state,
the early warning radar telling you the ZIP code, while the
[radars aboard the rocket] get you to the street address,"
said the official. "What we failed to do is ring the
doorbell."

The official said the infrared sensors guide the kill
vehicle in the final seconds of flight. The test -- called
integrated flight test 4 -- pitted the experimental
national missile defense system against a simulated warhead
launched aboard a Minuteman missile from Vandenberg Air
Force Base, Calif. The kill vehicle launched from Kwajalein
Missile Range in the Pacific.

The previous test vaporized the target with a direct hit.
The kill vehicle is the bullet of the weapon system. It
destroys a target using the kinetic energy of the force of
impact; there are no explosives involved. Had the test
worked, the kill vehicle and the target would have hit at
about 15,000 miles an hour.

Officials said that initially everything appeared to go
well. One objective of the test was to evaluate the kill
vehicle's deployment and orientation. The vehicle launched,
deployed and, using visual sensors, oriented it correctly,
officials said. "It was in 'the basket,'" said the
official.

Another goal was to demonstrate the ability of the space-
based sensors and ground-based radars to detect and acquire
a simulated threat, track the threat and discriminate using
the prototype ground-based x-band radar at Kwajalein. This,
too, worked well.

Finally, the test demonstrated the Battle Management
Command and Control and Communication system. This is the
nerve center of the system. It receives the information it
gathers from the space-based sensors and from radars and
then processes it. "Then it sets up the engagement and
provides real-time data communications directed to the
weapon," said the official. The system's performance was
"nominal" -- space talk for it worked well.

The test seemed to be a success until the last six seconds.
"It appears that there was an anomaly or an issue with the
infrared sensor packages," the official said. "This seeker
has two infrared sensors and one visual light. We have to
go figure out what happened to the IR sensors.

"As we're sitting there at 29 minutes, 49 seconds after the
target lifted off, there was not the bright flash that we
saw on the [previous test, indicating a hit]."

The prime contractor for the system is Boeing. Raytheon
built the exoatmospheric vehicle, and TRW built the Battle
Management Missile Command and Control and Communication
system. The test cost about $100 million. Ballistic Missile
Defense Organization officials along with the contractors
will examine the data from the test and make corrections as
needed. The official said DoD can "absolutely" overcome the
technical challenges of the program.